Disk drives are widely used in computers, consumer electronics and data processing systems for storing information in digital form. The disk drive typically includes one or more storage disks and one or more head suspension assemblies. Each head suspension assembly includes a slider having an air bearing surface, and a read/write head that transfers information to and from the storage disk. The rotation of the storage disk causes the slider to ride on an air bearing so that the read/write head is at a distance from the storage disk that is referred to as a “head-to-disk spacing”.
Because today's disk drives utilize storage disks having increasingly high densities of data tracks, decreasing the head-to-disk spacing has become of great importance. However, this desire for a very small head-to-disk spacing must be balanced with tribological concerns in order to avoid damage to the read/write head and/or the storage disk, as well as loss of data.
Further, a large variation in the head-to-disk spacing from slider to slider can cause significant issues in the manufacturing and reliability of the disk drives. Additionally, maintaining a relatively small and consistent head-to-disk spacing is further complicated by other factors. In particular, the read/write head includes a write head having a write element. During a write operation, the electrical resistance of the write element generates heat in and around the read/write head. The extent and rate of heating depends upon the level of current directed to the write element. This temperature increase causes thermal expansion of portions of the slider toward the storage disk, known as “write pole tip protrusion” or WPTP. If the write pole tip protrusion is too extensive, the slider can unintentionally contact the storage disk, causing off-track writing, damage to the slider, damage to the storage disk and/or a permanent loss of data.
Unfortunately, the ability to accurately determine the actual head-to-disk spacing in situ has been elusive. In conventional disk drives, only relative changes in head-to-disk spacing have been at least theoretically attainable.